Congratulations!
[name_f][/name_f]Both names are lovely however I do prefer [name_m]Marlow[/name_m] (this spelling) I think this spelling feels completely unisex and has the association of [name_m]Christopher[/name_m] [name_f]Marlowe[/name_f] which creates a masculine flair. Whereas for me [name_f]Marlo[/name_f] feels more feminine and makes me think of [name_f]Margo[/name_f], [name_f]Cleo[/name_f] etc. So yes to summarise [name_m]Marlow[/name_m] (or [name_f]Marlowe[/name_f] do prefer the more streamlined Marlow) with nickname [name_f]Marley[/name_f].
[name_f][/name_f]Wishing you all the best 